linux-kernel - RE: [PATCH v12 01/37] x86/cpufeatures: Add the cpu feature bit for WRMSRNS

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Message-ID: <SA1PR11MB67340C23AF350C8CB4119090A8B2A@SA1PR11MB6734.namprd11.prod.outlook.com>
Date:   Tue, 14 Nov 2023 05:58:32 +0000
From:   "Li, Xin3" <xin3.li@...el.com>
To:     Borislav Petkov <bp@...en8.de>
CC:     "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
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        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "Lutomirski, Andy" <luto@...nel.org>,
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        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
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        "nik.borisov@...e.com" <nik.borisov@...e.com>
Subject: RE: [PATCH v12 01/37] x86/cpufeatures: Add the cpu feature bit for
 WRMSRNS

> and if you had to be precise, the code should do:
> 
> 	if (cpu_feature_enabled(X86_FEATURE_FRED)) {
> 		if (cpu_feature_enabled(X86_FEATURE_WRMSRNS))
> 			wrmsrns(MSR_IA32_FRED_RSP0, (unsigned
> long)task_stack_page(task) + THREAD_SIZE);
> 		else
> 			wrmsr(MSR_IA32_FRED_RSP0, (unsigned
> long)task_stack_page(task) + THREAD_SIZE);
> 	}

This is exactly what tglx wanted to avoid.

And I love the idea "baseline", especially we have a ton of CPU features.

> 
> > Another patch set should replace WRMSR with WRMSRNS, with SERIALIZE
> > added when needed.
> 
> I sense someone wants to optimize MSR writes ... :-)

:-)